The invention relates to a method for operating an on-board electrical system for a motor vehicle, and to a motor vehicle comprising an on-board electrical system of this kind.
In motor vehicles comprising an internal combustion engine, an on-board electrical system, which is operated with 12 volts as standard, is provided for supplying electrical energy to the electrical starter for the internal combustion engine and to further devices in the motor vehicle. When the internal combustion engine is started, a voltage is provided from a starter battery, via the on-board electrical system, to a starter, which starts the internal combustion engine when a switch is closed, for example, by means of a corresponding starter signal. If the internal combustion engine has been started, it drives an electrical generator, which then generates a voltage of approximately 12 volts and provides said voltage, via the on-board electrical system, to the different electrical loads in the motor vehicle. In this case, the electrical generator also recharges the starter battery, which has been loaded by the starting operation. If the battery is charged via the on-board electrical system, the actual voltage can be above the nominal voltage, e.g., it can be 14 V or 14.4 V.
It is known to use a further on-board electrical system having a nominal voltage of 48 V in electric and hybrid vehicles.
U.S. Pat. No. 7,193,392 discloses a battery pack, which can accept charge from an HEV engine when the electric motor is driven as a generator by the HEV engine or is driven as a generator by the kinetic and potential energy of the motor vehicle during braking operations. A control unit provides energy to a pair of bidirectional switches in order to electronically couple a single battery cell to an equalization converter. The pair of switches is utilized for selectively charging and discharging individual battery cells.
U.S. Pat. No. 6,909,201 discloses a switchable voltage supply architecture for an on-board electrical system of a motor vehicle, wherein only one battery configuration is utilized, in order to reduce installation space, costs, and complexity. A bidirectional DC-to-DC converter functions as a down converter when a low-voltage electrical subsystem is supplied with current and, in another operating mode, can also function as an up converter when a high-voltage electrical subsystem is supplied with current.
U.S. Pat. No. 8,129,952 discloses a battery system comprising conversion circuitry and a plurality of main terminals configured to be connected to a load, a charger and a plurality of rechargeable battery modules which are connected in series to one another and are located between the main terminals. The battery system comprises switching circuitry which is configured such that a first of the battery modules is coupled to an input of the switching circuitry. The modules are also connected to a balance circuitry, wherein the balance circuitry is configured to receive electrical energy from a first of the rechargeable battery modules.